Using the analytical model we developed for an nth-order cascaded Raman laser, we find the design rules for such lasers. We determine analytical expressions for the cavity length and the output-coupler reflectivity that maximize the output power and minimize threshold power. Simple expressions are obtained in the depleted-pump approximation. Deviations from these expressions when the pump is not completely depleted are shown to be different depending on the parity of the number n of Stokes shifts (cascades). The design rules show that the mirror reflectivity is a critical factor in the laser quality and that the ultimate slope efficiency epsilon is found to be g_n/g_0. We also find a condition to determine if P-doped fibers are more useful than Ge-doped fibers in Raman fiber lasers based only on the Raman shift and absorption of the fibers.
© 2005 Optical Society of AmericaPDF Article